Traveling-wave tube having auxiliary resonant cavities containing lossy bodies which protrude into the slow-wave structure interaction cells to provide combined frequency sensitive and directionally sensitive attenuation

ABSTRACT

In the disclosed traveling-wave tube, auxiliary cavities which are resonant at a frequency in the vicinity of a cutoff frequency of the slow-wave structure communicate with respective slow-wave structure interaction cells. Lossy ceramic bodies disposed in respective auxiliary cavities protrude into the adjacent slowwave structure interaction cells to simultaneously provide both frequency sensitive and directionally sensitive attenuation. In a single section tube the distance of protrusion is essentially uniform for the respective lossy bodies. In a severed tube the distance of protrusion of successive lossy bodies in an amplifying section is progressively decreased as a function of longitudinal distance from the sever in order to additionally function to terminate the amplifying section.

United States Patent [72] Inventor .leflrey E. Grant Los Angeles. Cdll.

[2i] Appl. No. 798,646

[22] Filed Feb. I2, 1969 [45] Patented Aug. 31, I971 [73) AssigneeIlughu Ai'cr'llt Col-poly Culver City, Calif.

[54] TRAVELING-WAVE TUBE HAVING AUXILIARY RESONAN'I CAVI'I'IB CONTAININGLOSSY BODIES WHICH PRUIRUDE INTO THE SLOW- WAVE STRUCTURE INTERACTIONCELLS TO PROVIDE COMBINED FREQUENCY SENSITIVE AND DIREC'IIONALLYSENSITIVE A'I'IENUATION I6 Clnhns, 6 Drawhg Fl [52] US. Cl. SIS/3.5,

3 l 513.6, SIS/39.3

[5|] Int. Cl. H01] 25/34 [50] I leldoISeu-eh 31513.5,

(56] Reterencs Cited UNITED STATES PATENTS 3,22 l ,204 ll/l965 Hant etal. 31513.5

Primary Examiner-Herman Karl Saalbach Assistant Examiner-SaxfieldChatmon, Jr. Attorney.r.lames K. Haskell and Paul M. Coble f ABSTRACT:In the disclosed traveling-wave tube, auxiliary cavities which areresonant at a frequency in the vicinity of a cutoff frequency of theslow-wave structure communicate with respective slow-wave structureinteraction cells. Lossy ceramic bodies disposed in respective auxiliarycavities protrude into the adjacent slow-wave structure interactioncells to simultaneously provide both frequency sensitive anddirectionally sensitive attenuation. In a single section tube thedistance of protrusion is essentially uniform for the respective lossybodies. In a severed tube the distance of protrusion of successive lossybodies in an amplifying section is progressively decreased as a functionof longitudinal distance from the sever in order to additionallyfunction to terminate the amplifying section.

my 0 w I @J l i r F l l PATENTEU was] :91: 3.602166 sum 1 or 3 Afro/wayTRAVELING-WAVE TUBE HAVING AUXILIARY RESONANT CAVITIES CONTAINING LOSSYBODIES WHICH PROTRUDE INTO THE SLOW-WAVE STRUCTURE INTERACTION CELLS TOPROVIDE COMBINED FREQUENCY SENSITIVE AND DIREC'I'IONALLY SENSITIVEATTENUATION This invention relates generally to microwave devices, andit more particularly relates to traveling-wave tubes having means forsimultaneously providing both frequency sensitive attenuation anddirectionally sensitive attenuation in order to increase tube stability.The invention also provides, for traveling-wave tubes of the type whichare severed into a plurality of amplifying sections, a combinedfrequency sensitive loss introducing and amplifying section terminatingarrangement.

ln traveling-wave tubes a stream of electrons is caused to interact witha propagating electromagnetic wave in a manner which amplifies theelectromagnetic energy. In order to achieve such interaction, theelectromagnetic wave is propagated along a slow-wave structure, such asa conductive helix wound about the path of the electron stream or afolded waveguide type of structure in which a waveguide is effectivelywound back and forth across the path of the electrons. The slow-wavestructure provides a path of propagation for the electromagnetic wavewhich is considerably longer than the axial length of the structure, andhence, the traveling-wave may be made to effectively propagate at nearlythe velocity of the electron stream. The interactions between theelectrons in the stream and the traveling-wave cause velocitymodulations and bunching of the electrons in the stream. The net resultmay then be a transfer of energy from the electron beam to the wavetraveling along the slow-wave structure.

The present invention is concerned with traveling-wave tubes utilizingslow-wave structures of the coupled cavity, or interconnected cell,type. ln this type of slow-wave structure a series of interaction cells,or cavities, are disposed adjacent to each other sequentially along theaxis of the tube. The electron stream passes through each interactioncell, and electromagnetic coupling is provided between each cell and theelectron stream. Each interaction cell is also coupled to an adjacentcell by means of a coupling hole at the end wall defining the cell.Generally, the coupling holes between adjacent cells are alternatelydisposed on opposite sides of the axis of the tube, although variousother arrangements for staggering the coupling holes are possible andhave been employed. When the coupling holes are so arranged, a foldedwaveguide type of energy propagation results, with the traveling-waveenergy traversing the length of the tube by entering each interactioncell from one side, crossing the electron stream and then leaving thecell from the other side, thus traveling a sinuous, or serpentine,extended path.

One of the problems encountered in traveling-wave tubes of the coupledcavity variety, and especially high power tubes of this type, is atendency for the tube to oscillate at frequencies near the edges of thetube passband. This problem arises from the fact that for wide bandoperation the phase velocity of the slow-wave circuit wave and thevelocity of the electron beam should be essentially synchronized over aslarge a range of frequencies as possible; hence, these velocities arealso close to synchronism near the upper and lower cutoff frequencies ofthe tube. Since the interaction impedance is high and thecircuibto-transmission line match is poor at and in the vicinity of thecutofi' frequencies, the loop gain for the tube, or even for a sectionof the tube, may be sufl'iciently large for oscillations to start.

One technique which has been used to solve this oscillation probleminvolves coupling to the slow-wave structure interaction cells speciallydesigned external auxiliary cavities which are resonant at a frequencyin the vicinity of a cutoff frequency of the slow-wave structure andproviding lossy ceramic buttons in the external cavities in order toattenuate energy at the resonant frequency of the cavity. For furtherdetails as to this technique reference may be made to U.S. Pat. No. 3,22l ,204, entitled "Traveling-Wave Tube with Trap Means for PreventingOscillation at Unwanted Frequencies," issued Nov. 30, 1965 to Williaml-lant et al. and assigned to the assignee of the present invention.While this external lossy resonant cavity arrangement functionsexcellently to introduce frequency sensitive attenuation into theslow-wave structure, the introduced attenuation is relativelyinsensitive to the direction of propagation of the electromagnetic wavetraveling along the slow-wave structure.

Accordingly, it is an object of the present invention to provide atraveling-wave tube having means for simultaneously introducing bothfrequency sensitive attenuation and directionally sensitive attenuationinto the slow-wave structure of the tube.

It is a further object of the present invention to provide atraveling-wave tube of the type employing oscillation suppressing lossyresonant cavities coupled to slow-wave structure interaction cells andin which the slow-wave structure backward loss is increased relative tothe effective forward loss, thereby increasing tube stability.

As traveling-wave tubes are designed for operation at higher and higherpower levels, in order to ensure stability such tubes have beenconstructed in several amplifying sections, with a substantiallycomplete sever or electromagnetic circuit wave isolation providedbetween adjacent amplifying sections, and the only coupling between thesections occurring by means of the velocity modulated electron stream.Since each amplifying section has a length appropriate for maximumstable gain, it is necessary to effectively terminate each section witha matched load. In the past such termination has been achieved byproviding separate terminating elements either internally of theslow-wave structure, externally of the slow-wave structure, or in hybridfashion both internally and externally of the slowwave structure. Forfurther details as to these terminations reference may be made to U.S.Pat. No. 2,985,791, entitled Periodically Focused Severed Traveling-WaveTube, issued May 23, 196i to David .I. Bates et al.; to U.S. Pat. No.3,123,736, entitled Severed Traveling-Wave Tube With ExternalTerminations," issued Mar. 3, 1964 to William H. Christolfers et al.;and to U.S. Pat. No. 3,l8l,023, entitled Severed Traveling-Wave TubeWith Hybrid Terminations," issued Apr. 27, 1965 to William Hant et al.,all of these patents being assigned to the assignee of the presentinvention.

It is a further object of the present invention to provide, for atraveling-wave tube of the type which is severed into a plurality ofamplifying sections, means for simultaneously providing both frequencysensitive attenuation and a terminating sever for respective amplifyingsections.

it is a still further object of the present invention to provide asevered traveling-wave tube which for comparable power handlingcapabilities is more compact than severed tubes having terminationarrangements according to the prior art.

it is still another object of the present invention to provide a severedtraveling-wave tube which can handle more RF power than comparablydimensioned traveling-wave tubes having prior art terminationarrangements.

lt is yet another object of the present invention to provide a severedtraveling-wave tube which provides an improved match at the severed endsof the amplifying sections, thereby reducing undesired small signal gainvariations as a function of frequency.

in accordance with the above objects, a traveling-wave tube according tothe present invention includes means for providing a stream of electronsalong a predetermined path and a slow-wave structure having a pluralityof intercoupled interaction cells disposed sequentially along and aboutthe electron stream path for propagating electromagnetic wave energy insuch manner that it interacts with the stream of electrons. A pluralityof cavities are respectively disposed externally of at least selectedones of the interaction cells and sequentially along a directionparallel to the electron stream path. Each cavity communicates with oneof the interaction cells and is resonant at a preselected frequency. Abody of lossy material is disposed in each cavity and protrudes into theadjacent interaction cell by a preselected distance.

In one embodiment of the invention the distance of protrusion isessentially the same for each lossy body. In this arrange ment thecavity resonances and the portions of the lossy bodies within thecavities provide frequency sensitive attenuation, while the protrudingportions of the lossy bodies introduce directionally sensitiveattenuation to the electromagnetic wave propagating along the slow-wavestructure.

In another embodiment of the present invention the traveling-wave tubeis severed into a plurality of amplifying sections. The distance ofprotrusion of successive ones of the lossy bodies in at least one of theamplifying sections is progressively decreased as a function oflongitudinal distance from the severed end of this amplifying section.The cavity resonances and the portions of the lossy bodies within thecavities introduce frequency sensitive attenuation, while theprogressively varying protrusion of the lossy bodies provides taperedattenuation which terminates the slow-wave structure amplifying section.

The foregoing, as well as other objects, advantages, and characteristicfeatures of the present invention will become more readily apparent fromthe following detailed description of preferred embodiments of theinvention when considered in conjunction with the accompanying drawingsin which:

FIG. I is an overall view, partly in longitudinal section and partlybroken away, of a single-section traveling-wave tube constructed inaccordance with one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a longitudinal sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a longitudinal sectional view taken along line 4-4 of FIG. 2',

FIG. 5 is an overall view, partly in longitudinal section and partlybroken away, of a severed traveling-wave tube constructed in accordancewith another embodiment of the present invention; and

FIG. 6 is a perspective view of a portion of the slow-wave structure,including the combined frequency sensitive loss introducing and sectionterminating arrangement of the invention, for the traveling-wave tube ofFIG. 5.

Referring to the drawings with more particularity, in FIG. 1 thereference numeral I0 designates generally a travelingwave tube whichincludes an arrangement 12 of magnets, pole pieces and spacer elementswhich will be described in detail later. At this point it should sufficeto state that the spacer elements and interior portions of the polepieces function as a slow-wave structure, while the magnets and polepieces can stitute a periodic focusing device for the electron beamtraversing the length of the slow-wave structure.

Coupled to the input end of the arrangement 12 is an input waveguidetransducer 14 which includes an impedance step transformer I6. A flange18 is provided for coupling the as sembled traveling-wave tube to anexternal waveguide or other microwave transmission line (not shown). Theconstruction of the flange l8 may include a microwave window (not shown)transparent to microwave energy but capable of maintaining a vacuumwithin the traveling-wave tube 10. At the output end of the arrangement12 an output transducer 20 is provided which is substantially similar tothe input transducer 14 and which includes an impedance step transformer22 and a coupling flange 24, which elements are similar to the elementsl6 and I8, respectively, of the input transducer I4. For vacuum pumpingor out-gassing the traveling-wave tube 10 during manufacture, adouble-ended pumping tube 26 is connected to both of the input andoutput waveguide transducers l4 and 20.

An electron gun 28 is disposed at one end of the travelingwave tube 10which, although illustrated as the input end in NO. I, may alternativelybe the output end if a backward wave device is desired. The electron gun28 functions to project a stream of electrons along the axis of the tube10 and may be of any conventional construction well known in the art.For details as to the construction of the gun 28 reference is made tothe aforementioned U.S. Pat. No. 2,985,791 and to U.S. Pat. No.2,936,393, entitled, "Low Noise Traveling- Wave Tube, issued May I0,1960, to M. R. Currie et al. and also assigned to the assignee of thepresent invention.

At the output end of the traveling-wave tube I0 there is provided acooled collector structure 30 for collecting the electrons in thestream. The collector is conventional and may be of any fonn well knownin the art. For details as to the construction of the collector,reference is made to the aforesaid U.S. Pat. No. 2,985,791 and to U.S.Pat. No. 2,860,277, entitled, Traveling-Wave Tube Collector Electrode,issued Nov. l l, P 8, to A. H. lversen and assigned to the assignee ofthe present invention.

The construction of the slow-wave structure and magnetic focusing systemfor the traveling-wave tube 10 are illustrated in more detail in FIGS.2-4. A plurality of essentially annular disk-shaped focusing magnets 32are interposed between a plurality of ferromagnetic pole pieces, orplates, 34. As is illustrated in FIG. 2, the magnets 32 may bediametrically split into two sections 320 and 32b for convenience duringassembly of the tube. The ferromagnetic pole pieces 34 extend radiallyinwardly of the magnets 32 to approximately the perimeter of the regionadapted to contain the axial electron stream. The individual pole piecesare constructed in such a manner that a short drift tube, or ferrule, 36is provided at the inner extremity of each pole piece. The drift tube 36is in the form of a cylindrical extension, or lip, protruding axiallyalong the path of the electron stream from both surfaces of pole piece34, Le, in both directions normal to the plane of the pole piece 34. Thedrift tubes 36 are provided with central and axially aligned apertures38 to provide a passage for the flow of the electron beam. Adjacent onesof the drift tubes 36 are separated by a gap 40 which functions as amagnetic gap to provide a focusing lens for the electron beam and alsoas an interaction gap in which energy exchange between the electron beamand traveling-wave energy traversing the slow-wave structure occurs.

Disposed radially within each of the magnets 32 is a slowwave circuitspacer element 42 of a conductive nonmagnetic material such as copper.Each spacer element 42 has an annular portion of an outer diameteressentially equal to the inner diameter of the magnets 32 and a pair ofoppositely disposed ear portions 43 and 44 projecting outwardly from theannular portion. Each spacer element also defines a central cylindricalaperture 45 to provide space for a microwave interaction cell, orcavity, 46 which is defined by the inner lateral surface of the spacer42 and the walls of the two adjacent pole pieces 34 projecting inwardlyof the spacer element 42. The inner diameter of the spacer 42 determinesthe radial extent of the interaction cell 46, while the axial length ofthe spacer 42 determines the axial length of the cell 46.

For interconnecting adjacent interaction cavities 46 an offcentercoupling hole 48 is provided through each of the pole pieces 34 topermit the transfer of electromagnetic wave energy from cell to cell. Asis illustrated, the coupling holes 48 may be substantially kidney-shapedand may be alternately disposed apart with respect to the drift tubes36. It should be pointed out, however, that the coupling holes 48 may beof other shapes and may be staggered in various other arrangements, suchas those disclosed in U.S. Pat. No. 3,010,047, entitled Traveling-WaveTube," issued Nov. 2i, I961 to D. .l. Bates and assigned to the assigneeof the present invention. In any event, it will be apparent that thespacer elements 42 and the portions of the pole pieces 34 projectinginwardly of the spacers 42 not only form an envelope for the tube, butalso constitute a slow-wave structure for propagating travelingwaveenergy in a serpentine path along the axially traveling electron streamso as to support energy exchange between the electrons of the stream andthe traveling-wave.

The axial length of the magnets 32, hence that of the spacers 42, isequal to the spacing between adjacent pole pieces 34, and the radialextent of the magnets 32 is approximately equal to or, as shown,slightly greater than that of the pole pieces 34. To provide focusinglenses in the gaps 40, the magnets 32 are stacked with alternatingpolarity along the axis of the tube, thus causing a reversal of themagnetic field at each magnetic lens and thereby providing a periodicfocusing device. It should be pointed out, however, that although thelengths of the spacers 42 may be substantially constant, they may alsobe varied slightly with respect to each other so that the effectiveaxial length of the cavities 46 is varied as a function of distancealong the tube to ensure that the desired interaction between theelectron stream and the traveling waves will continue to a maximumdegree even though the electrons are decelerated toward the collectorend of tube.

In order to minimize any tendency for the traveling-wave tube tooscillate at frequencies near the edges of the slowwave circuitpassband, frequency selective attenuation is provided to substantiallydecrease the gain at these frequencies and, thereby, suppress theoscillations. This attenuation takes the form of lossy ceramic bodiesdisposed in cavities which are coupled to the slow-wave structureinteraction cells and which cavities are made resonant at thefrequencies to be attenuated. Thus, as is shown in FIGS. 2 and 4, aslow-wave structure spacer element 42 may define a pair of cylindricalcavities 50 and 52 which are respectively disposed in the projecting earportions 43 and 4-4 of the spacer element 42 and have their longitudinalaxes disposed parallel to the longitudinal axis of the traveling-wavetube I2. The cavities and 52 have a length equal to the thickness of theslow-wave structure spacer element 42 and are designed to resonate at afrequency at which loss is to be introduced into the circuit. Althoughthe cavity resonant frequency is preferably at or near either the upperor lower cutoff frequency of the slow-wave structure, it is to beunderstood that the resonant loss frequency may be any preselectedfrequency. Cylindrical buttonlike bodies 54 and 56 of a mixture ofceramic and lossy materials are disposed in and substantially fill therespective cavities 50 and 52 in order to provide the desired loss. Forfurther details as to the resonant cavities 50 and 52 and the lossybodies 54 and 56 reference may be made to the aforementioned US. Pat.No. 3,221,204.

As is illustrated in FIG. 2, the lossy bodies 54 and 56 protrude intothe adjacent interaction cell 46 by a preselected distance d. Thedistance of protrusion d is preferably between percent and 30 percent ofthe distance from the edge of the interaction cell 46 to the center ofthe stream of electrons, ie the radius r of the interaction cell.

In the embodiment of FIGS. 1-4, the traveling-wave tube has a singleamplifying section, and the distance of protrusion d of each of thelossy bodies 54 (or 56) is essentially the same. Thus, essentiallyuniform distributed attenuation is introduced to the slow-wavestructure. This distributed loss attenuates electromagnetic wavestraversing the slow-wave structure in the backward direction, i.e. fromthe collector 30 toward the electron gun 28, by two to three times morethan it attenuates electromagnetic waves traveling in the forwarddirection, i.e. from the electron gun 28 toward the collector 30. Thus,the resonant cavities 50 and 52 and the protmding lossy bodies 54 and 56function to provide both frequency sensitive attenuation at the cavityresonant frequency and directionally sensitive attenuation in favor offorwardly traveling electromagnetic waves, thereby increasing thestability of the tube.

In the embodiment of the invention illustrated in FIGS. 5 and 6, thetraveling-wave tube is severed into a plurality of amplifying sections.Since the traveling-wave tube of FIGS. 5 and 6 is very similar to thatof FIGS. 14, components in the embodiment of FIGS. 5-6 which are thesame as corresponding components in the embodiment of FIGS. I4 aredesignated by the same second and third reference numeral digits astheir corresponding components in FIGS. 1-4 but with the addition of theprefix numeral l."

In the embodiment of FIGS. 5-6 the traveling-wave tube I10 isillustrated as having three amplifying sections 162, 164 and 166,although it is understood that three such sections are shown solely forillustrative purposes. Each of the amplifying sections is isolated fromthe adjacent section or sections by means of an isolator device. Thus,in the traveling-wave tube shown in FIG. 5, the first and secondamplifying sections 162 and 164, respectively, are isolated from eachother by isolator device I68; while the second and third amplifyingsections I64 and 166, respectively, are isolated from one another bymeans of isolator device 170. The isolator devices 168 and I70 provide asubstantially complete sever between adjacent amplifying sections of thetraveling-wave tube IIO for electromagnetic waves traveling along theslow-wave structure, and which waves are hereinafter referred to aselectromagnetic circuit waves. At the same time the electron stream isallowed to pass through the entire length of the traveling-wave tube110. The electron stream is modulated in each amplifying section, andhence, as it enters the subsequent amplifying section it launches a newelectromagnetic circuit wave therein which is amplified by interactionbetween the new electromagnetic circuit wave and the electron stream.Thus, unidirectional coupling adjacent amplifying sections is providedby means of the electron stream.

FIG. 5 is broken away in the region of isolator device 170 in order toillustrate the interior construction thereof, it being understood thatisolator device I68 is constructed in an identical manner. Isolatordevice 170 comprises a modified pole piece, or plate, 134 which differsfrom the remaining pole pieces 134 in that no coupling hold forelectromagnetic circuit waves is provided in the pole piece I34. Thisprevents electromagnetic circuit waves in amplifying section 164 frompassing into the section 166, and vice versa, thereby achievingelectromagnetic circuit wave isolation between the sections 164 and 166.

The interior portion of slow-wave structure amplifying section 164adjacent isolator device I70 is illustrated in FIG. 6. It may be seenthat the distance of protrusion of successive lossy bodies 1540, 154b,I54c and 154d (also 1560, 156b, l56c and 156d) disposed in respectivespacer elements 142a, I42b, I42c and 146d into respective interactioncells 146a, I46b, l46c and 146d decreases as a function of longitudinaldistance from the isolator pole piece 134. The distance of protrusioncan be varied by varying the radial location of successive lossy bodieswith respect to the tube axis. However, in a preferred arrangement,illustrated in FIG. 6, the successive lossy bodies are axially alignedwith one another and their distance of protrusion into the respectiveinteraction cells is varied by removing varying portions of the lossybodies on the side facing the stream of electrons. Thus, in FIG. 6 lossybodies I54b, 154a and 154d (also 156b, l56c and 156d) define respectiveflat, or planar, lateral surfaces b, ISSc and I55d (I57b, 157C and 157d)facing the stream of electrons in respective planes perpendicular to theplane passing through the longitudinal axes of the lossy bodies and theelectron stream path. The distance between the respective planes of thesurfaces 155b, 1556 and 155d (also 157b, l57c and 157d) and the outeredge of the respective interaction cells 146b, 1460 and 146d isprogressively decreased as a function of longitudinal distance from theisolator pole piece I34. In a preferred embodiment of the invention thedistance of protrusion d of the successive lossy bodies is decreasedessentially linearly as a function of longitudinal distance from theisolator pole piece 134', although it should be understood that otherrelationships are possible and may be employed.

Since the distance of protrusion of the lossy bodies determines theamount of attenuation introduced to the slow-wave structure, with thegreater the protrusion the greater the loss, the arrangement of FIG. 6provides progressively increasing attenuation as a function of distancetoward isolator pole piece 134'. Thus, the end of the amplifying sectionI64 adjacent the isolator pole piece I34 is effectively terminated withminimum reflection of electromagnetic circuit wave energy back towardthe electron gun 128. As a result, undesired small signal gainvariations as a function of frequency are minimized. In addition, sincethe auxiliary resonant cavities and the protruding lossy bodies performthe combined functions of providing both frequency sensitive attenuationand a terminating sever (which functions required separate attenuatingand terminating elements in the prior art), a severed traveling-wavetube according to the present invention requires fewer parts and is morecompact than prior art severed tubes with comparable power handlingcapabilities. Moreover, a severed traveling-wave tube according to theinvention is able to handle more RF power than comparably dimensionedsevered traveling-wave tubes according to the prior art.

It is pointed out that the arrangement illustrated in FIG. 6 is designedto provide a termination for forwardly traveling electromagnetic circuitwaves in amplifying section 164. The same arrangement may be employed atthe end of amplifying section 162 adjacent isolator device 168 toprovide a termination for forwardly traveling electromagnetic circuitwaves in the section 162. Moreover, a similar arrangement can be sued ineach of the sections 162, 164 and 166 to provide a termination forbackwardly traveling electromagnetic circuit waves. In such anarrangement the distance of protrusion of successive lossy bodies wouldbe decreased as a function of distance from the ends of the respectiveamplifying sections nearest the electron gun l28 in a direction towardthe collector 130. Thus, in sections 162 and 164 the lossy bodyprotrusion would be the greatest at both ends and smallest at thelongitudinal centers of these amplifying sections.

Although the present invention has been shown and described withreference to particular embodiments, nevertheless various changes andmodifications which are obvious to a person skilled in the relevant artare deemed to lie within the purview of the invention.

What l claim is:

l. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path, slow-wave structure means defininga plurality of intercoupled interaction cells disposed sequentiallyalong and about said predetermined path for propagating electromagneticwave energy in such manner that it interacts with said stream ofelectrons, means defining a plurality of cavities respectively disposedexternally of at least selected ones of said interaction cells andsequentially along a direction parallel to said predetermined path, eachof said cavities communicating with one of said interaction cells andbeing resonant at a preselected frequency, and a body of lossy materialdisposed in each said cavity and protruding into the adjacent one ofsaid interaction cells by a preselected distance.

2. A traveling-wave tube according to claim I wherein said cavities andsaid bodies are of essentially cylindrical shape and have theirlongitudinal axes disposed parallel to said predetermined path.

3. A traveling-wave tube according to claim 1 wherein said preselecteddistance of protrusion is between essentially 5 percent and essentially30 percent of the distance from the edge of said interaction cell to thecenter of said stream of electrons.

4. A traveling-wave tube according to claim 1 wherein said preselecteddistance of protrusion is essentially the same for each of said bodies.

5. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path, a plurality of axially alignedessentially annular electrically conductive spacer elements sequentiallydisposed along and encompassing said predetermined path, a plurality ofelectrically conductive plates each mounted between a pair of adjacentspacer elements to define in conjunction with said spacer elements aplurality of interaction cells, said plates defining aligned aperturesin their central regions to provide a passage for said electron streamand further defining coupling holes in regions radially outwardly ofsaid central regions for interconnecting adjacent interaction cellswhereby a propagation path is provided for an electromagnetic wave in amanner to provide interaction between said electron stream and saidelectromagnetic wave, at least certain ones of said spacer elements eachdefining a cavity disposed externally of and communicating with theinteraction cell defined by the said spacer element, each of saidcavities being resonant at a preselected frequency, and a body of lossymaterial disposed in each said cavity and protruding into the adjacentinteraction cell by a preselected distance.

6. A traveling-wave tube according to claim 5 wherein each said cavityand each said body is of essentially cylindrical shape and has itslongitudinal axis disposed parallel to said preselected path.

7. A traveling-wave tube according to claim 5 wherein said preselecteddistance of protrusion is between essentially 5 percent and essentially30 percent of the radius of said interaction cell.

8. A traveling-wave tube according to claim 5 wherein said preselecteddistance of protrusion is essentially the same for each said body.

9. A traveling-wave tube of the type which is severed into a pluralityof amplifying sections, each isolated from one another with respect toelectromagnetic circuit wave energy, comprising: means for providing astream of electrons along a predetermined path, slow-wave structuremeans extending through each of said amplifying sections and defining aplurality of intercoupled interaction cells disposed sequentially alongand about said predetermined path for propagating elec tromagneticcircuit wave energy in such manner that it interacts with said stream ofelectrons, means disposed between each pair of adjacent amplifyingsections for precluding the passage of electromagnetic circuit waveenergy between said adjacent amplifying sections while permitting thepassage of said stream of electrons therebetween, means defining aplurality of cavities respectively disposed externally of at leastselected ones of said interaction cells and sequentially along adirection parallel to said predetermined path, each of said cavitiescommunicating with one of said interaction cells and being resonant at apreselected frequency, and a body of lossy material disposed in eachsaid cavity and protruding into the adjacent one of said interactioncells by a preselected distance, the distance of protrusion ofsuccessive ones of bodies in at least one of said amplifying sectionsprogressively decreasing as a function of longitudinal distance from theend of said one amplifying section adjacent said precluding means.

10. A traveling-wave tube according to claim 9 wherein the distance ofprotrusion of successive ones of said bodies in said one amplifyingsection decreases essentially linearly as a function of longitudinaldistance from said end of said amplifying section.

ll. A traveling-wave tube according to claim 9 wherein said cavities andsaid bodies are of essentially cylindrical shape and have theirlongitudinal axes disposed parallel to said predetermined path.

12. A traveling-wave tube according to claim ll wherein at leastselected ones of said bodies in said one amplifying section each definea planar lateral surface facing said stream of electrons and in a planeessentially perpendicular to the plane passing through the longitudinalaxes of the said body and said predetermined path, the distance betweenthe plane of said surface and the edge of the interaction cell intowhich the said body protrudes progressively decreasing as a function oflongitudinal distance from the end of said one amplifying sectionadjacent said precluding means.

13. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path; a wave propagating structuredivided into at least first and second amplifying sections and disposedalong and about said predetermined path, each of said sections includinga plurality of axially aligned essentially annular electricallyconductive spacer elements sequentially disposed along and encompassingsaid predetermined path, a plurality of electrically conductive plateseach mounted between a pair of adjacent spacer elements to define inconjunction with said spacer elements a plurality of interaction cells,said plates defining aligned apertures in their central regions toprovide a passage for said electron stream and further defining couplingholes in regions radially outwardly of said central regions forinterconnecting adjacent interaction cells whereby a propagation path isprovided for an electromagnetic circuit wave in a manner to provideinteraction between said electron stream and said electromagneticcircuit wave; an isolator electrically conductive plate similar to theplates of said plurality but not defining any electromagnetic circuitwave coupling hole disposed between said first and second amplifyingsections and axially aligned with the remainder of said plates, wherebythe passage of electromagnetic circuit waves between said first andsecond amplifying sections is precluded while the passage of saidelectron stream therebetween is permitted; at least certain ones of saidspacer elements each defining a cavity disposed externally of andcommunicating with the interaction cell defined by the said spacerelement, each of said cavities being resonant at a preselectedfrequency; and a body of lossy material disposed in each said cavity andprotruding into the adjacent interaction cell by a preselected distance.the distance of protrusion of successive ones of said bodies in at leastone of said amplifying sections progressively decreasing as a functionof longitudinal distance from said isolator plate.

14. A traveling-wave tube according to claim 13 wherein the distance ofprotrusion of successive ones of said bodies in said one amplifyingsection decreases essentially linearly as a function of longitudinaldistance from said isolator plate.

15. A traveling-wave tube according to claim 13 wherein said cavitiesand said bodies are of essentially cylindrical shape and have theirlongitudinal axes disposed parallel to said predetermined path.

16. A traveling-wave tube according to claim l5 wherein at leastselected ones of said bodies in said one amplifying section each definea planar lateral surface facing said stream of electrons and in a planeessentially perpendicular to the plane passing through the longitudinalaxes of the said body and said predetermined path, the distance betweenthe plane of said surface and the edge of the interaction cell into thesaid body protrudes progressively decreasing as a function oflongitudinal distance from said isolator plate.

1. A traveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path, slow-wave structure means defininga plurality of intercoupled interaction cells disposed sequentiallyalong and about said predetermined path for propagating electromagneticwave energy in such manner that it interacts with said stream ofelectrons, means defining a plurality of cavities respectively disposedexternally of at least selected ones of said interaction cells andsequentially along a direction parallel to said predetermined path, eachof said cavities communicating with one of said interaction cells andbeing resonant at a preselected frequency, and a body of lossy materialdisposed in each said cavity and protruding into the adjacent one ofsaid interaction cells by a preselected distance.
 2. A traveling-wavetube according to claim 1 wherein said cavities and said bodies are ofessentially cylindrical shape and have their longitudinal axes disposedparallel to said predetermined path.
 3. A traveling-wave tube accordingto claim 1 wherein said preselected distance of protrusion is betweenessentially 5 percent and essentially 30 percent of the distance fromthe edge of said interaction cell to the center of said stream ofelectrons.
 4. A traveling-wave tube according to claim 1 wherein saidpreselected distance of protrusion is essentially the same for each ofsaid bodies.
 5. A traveling-wave tube comprising: means for providing astream of electrons along a predetermined path, a plurality of axiallyaligned essentially annular electrically conductive spacer elementssequentially disposed along and encompassing said predetermined path, aplurality of electrically conductive plates each mounted between a pairof adjacent spacer elements to define in conjunction with said spacerelements a plurality of interaction cells, said plates defining alignedapertures in their central regions to provide a passage for saidelectron stream and further defining coupling holes in regions radiallyoutwardly of said central regions for interconnecting adjacentinteraction cells whereby a propagation path is provided for anelectromagnetic wave in a manner to provide interaction between saidelectron stream and said electromagnetic wave, at least certain ones ofsaid spacer elements each defining a cavity disposed externally of andcommunicating with the interaction cell defined by the said spacerelement, each Of said cavities being resonant at a preselectedfrequency, and a body of lossy material disposed in each said cavity andprotruding into the adjacent interaction cell by a preselected distance.6. A traveling-wave tube according to claim 5 wherein each said cavityand each said body is of essentially cylindrical shape and has itslongitudinal axis disposed parallel to said preselected path.
 7. Atraveling-wave tube according to claim 5 wherein said preselecteddistance of protrusion is between essentially 5 percent and essentially30 percent of the radius of said interaction cell.
 8. A traveling-wavetube according to claim 5 wherein said preselected distance ofprotrusion is essentially the same for each said body.
 9. Atraveling-wave tube of the type which is severed into a plurality ofamplifying sections, each isolated from one another with respect toelectromagnetic circuit wave energy, comprising: means for providing astream of electrons along a predetermined path, slow-wave structuremeans extending through each of said amplifying sections and defining aplurality of intercoupled interaction cells disposed sequentially alongand about said predetermined path for propagating electromagneticcircuit wave energy in such manner that it interacts with said stream ofelectrons, means disposed between each pair of adjacent amplifyingsections for precluding the passage of electromagnetic circuit waveenergy between said adjacent amplifying sections while permitting thepassage of said stream of electrons therebetween, means defining aplurality of cavities respectively disposed externally of at leastselected ones of said interaction cells and sequentially along adirection parallel to said predetermined path, each of said cavitiescommunicating with one of said interaction cells and being resonant at apreselected frequency, and a body of lossy material disposed in eachsaid cavity and protruding into the adjacent one of said interactioncells by a preselected distance, the distance of protrusion ofsuccessive ones of bodies in at least one of said amplifying sectionsprogressively decreasing as a function of longitudinal distance from theend of said one amplifying section adjacent said precluding means.
 10. Atraveling-wave tube according to claim 9 wherein the distance ofprotrusion of successive ones of said bodies in said one amplifyingsection decreases essentially linearly as a function of longitudinaldistance from said end of said amplifying section.
 11. A traveling-wavetube according to claim 9 wherein said cavities and said bodies are ofessentially cylindrical shape and have their longitudinal axes disposedparallel to said predetermined path.
 12. A traveling-wave tube accordingto claim 11 wherein at least selected ones of said bodies in said oneamplifying section each define a planar lateral surface facing saidstream of electrons and in a plane essentially perpendicular to theplane passing through the longitudinal axes of the said body and saidpredetermined path, the distance between the plane of said surface andthe edge of the interaction cell into which the said body protrudesprogressively decreasing as a function of longitudinal distance from theend of said one amplifying section adjacent said precluding means.
 13. Atraveling-wave tube comprising: means for providing a stream ofelectrons along a predetermined path; a wave propagating structuredivided into at least first and second amplifying sections and disposedalong and about said predetermined path, each of said sections includinga plurality of axially aligned essentially annular electricallyconductive spacer elements sequentially disposed along and encompassingsaid predetermined path, a plurality of electrically conductive plateseach mounted between a pair of adjacent spacer elements to define inconjunction with said spacer elements a plurality of interaction cells,said plates defining aligned apertures in their central regions toprovide a Passage for said electron stream and further defining couplingholes in regions radially outwardly of said central regions forinterconnecting adjacent interaction cells whereby a propagation path isprovided for an electromagnetic circuit wave in a manner to provideinteraction between said electron stream and said electromagneticcircuit wave; an isolator electrically conductive plate similar to theplates of said plurality but not defining any electromagnetic circuitwave coupling hole disposed between said first and second amplifyingsections and axially aligned with the remainder of said plates, wherebythe passage of electromagnetic circuit waves between said first andsecond amplifying sections is precluded while the passage of saidelectron stream therebetween is permitted; at least certain ones of saidspacer elements each defining a cavity disposed externally of andcommunicating with the interaction cell defined by the said spacerelement, each of said cavities being resonant at a preselectedfrequency; and a body of lossy material disposed in each said cavity andprotruding into the adjacent interaction cell by a preselected distance,the distance of protrusion of successive ones of said bodies in at leastone of said amplifying sections progressively decreasing as a functionof longitudinal distance from said isolator plate.
 14. A traveling-wavetube according to claim 13 wherein the distance of protrusion ofsuccessive ones of said bodies in said one amplifying section decreasesessentially linearly as a function of longitudinal distance from saidisolator plate.
 15. A traveling-wave tube according to claim 13 whereinsaid cavities and said bodies are of essentially cylindrical shape andhave their longitudinal axes disposed parallel to said predeterminedpath.
 16. A traveling-wave tube according to claim 15 wherein at leastselected ones of said bodies in said one amplifying section each definea planar lateral surface facing said stream of electrons and in a planeessentially perpendicular to the plane passing through the longitudinalaxes of the said body and said predetermined path, the distance betweenthe plane of said surface and the edge of the interaction cell into thesaid body protrudes progressively decreasing as a function oflongitudinal distance from said isolator plate.